Interstate 15 (I-15) is a major

Interstate Highway The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, or the Eisenhower Interstate System, is a network of controlled-access highways that forms part of the National Hi ...

in the

Western United States The Western United States (also called the American West, the Western States, the Far West, the Western territories, and the West) is List of regions of the United States, census regions United States Census Bureau. As American settlement i ...

, running through

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...

and the Intermountain West. I-15 begins near the Mexican border in San Diego County and stretches north to Alberta, Canada, passing through the states of

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...

, and

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

. The Interstate serves the cities of

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

, San Bernardino,

Las Vegas Las Vegas, colloquially referred to as Vegas, is the most populous city in the U.S. state of Nevada and the county seat of Clark County. The Las Vegas Valley metropolitan area is the largest within the greater Mojave Desert, and second-l ...

Salt Lake City Salt Lake City, often shortened to Salt Lake or SLC, is the capital and most populous city of the U.S. state of Utah. It is the county seat of Salt Lake County, the most populous county in the state. The city is the core of the Salt Lake Ci ...

, Idaho Falls, and Great Falls. It also passes close to the urban areas of

Los Angeles Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...

, Orange, and Riverside counties in California. The stretches of I-15 in Idaho, Utah, and Arizona have been designated as the "Veterans Memorial Highway". The southern end is at a junction with I-8 and State Route 15 (SR 15) in San Diego, and the northern end is at a connection with Alberta Highway 4 at the Sweetgrass–Coutts Border Crossing. I-15 was built to connect the Inland Empire with San Diego in California, facilitate tourism access to Las Vegas, provide access to the Arizona Strip, interconnect all of the metropolitan statistical areas in Utah except for Logan, and provide freeway bypasses for Pocatello, Idaho Falls, and Great Falls. Since its creation, I-15 has served as a long-haul route for

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

n commerce. It is now officially chartered for this purpose: from the junction of I-11 in

to the Canadian border, I-15 forms part of the CANAMEX Corridor, a High Priority Corridor, as a result of the North American Free Trade Agreement. Since the construction of I-15, California, Idaho, Nevada, and Utah have consistently ranked in the fastest-growing areas of the United States. As a result, the route of I-15 has substantially increased in population and commuter traffic.

Route description

, - , CA , , - , NV , , - , AZ , , - , UT , , - , ID , , - , MT , , - , Total , This highway's southern terminus is in

San Diego, California San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

, at I-8, although via SR 15, a southern extension of the freeway, the route connects to I-5 12.5 miles from the US/Mexico border in southern San Diego. The northern terminus is in Sweet Grass, Montana, at the Canada–US border, where it becomes Alberta Highway 4. It is long from San Diego to Sweet Grass.

California

North of its junction with SR 91 in Corona, the route roughly follows the former routes of State Route 31. North of Devore, the highway follows the approximate alignment of historic US Route 66 along with US 91 and US 395. US 395 breaks away at Hesperia and the route continues on a direct path to Barstow to the north. Meanwhile, the old alignments of US 91 and US 66 follow the Mojave River from Victorville to Barstow along the National Trails Highway. At that point, I-15 follows the old route of US 91 exclusively as US 66 turned east toward Needles. For many parts of the highway, high-voltage powerlines, such as Path 46 and Path 27, almost all originating from the Hoover Dam, follow the freeway. Many of these link distant power stations to the

metropolitan area. The southern starting point of I-15 was in 1957 planned to be in San Bernardino, at the interchange with the San Bernardino Freeway (then US 70/US 99, now I-10). This was logical as I-15 was following the old alignment of the historic Route 66 which passed through San Bernardino. The segment was completed accordingly. In 1964, legislation was later passed to extend the Interstate to

. Instead of extending the existing freeway from the I-10 interchange south, however, the California Department of Transportation drew a new segment in Devore that "branched" off of the original alignment and bypassed San Bernardino altogether. This segment's alignment is generally northeast to southwest for about . Then, in Rancho Cucamonga, its directional alignment shifts to north–south where it eventually meets with I-10 (about west of the original interchange in San Bernardino). The segment that had been built from Devore to San Bernardino was retained as an Interstate, but was renumbered as I-215. Note that during the construction of I-15's present alignment, and for some time afterward, I-215 was numbered as I-15E, and its actual mileage would begin at I-10. I-15 runs for a total of in California.

Nevada

I-15 begins in Primm and continues through

along the Las Vegas Strip corridor. Then, the Interstate crosses the border with

in Mesquite. The Interstate in

runs entirely in Clark County, for a distance of .

Arizona

I-15 passes through the northwestern corner of

with a total length of . The stretch is separated from the rest of the state and has one major exit, at

Beaver Dam A beaver dam or beaver impoundment is a dam built by beavers; it creates a pond which protects against predators such as coyotes, alligators, cougars, foxes, eagles, wolves and bears, and holds their food during winter. These structures modify th ...

/ Littlefield, Arizona. It includes a spectacular section where the road twists between the narrow walls of the Virgin River Gorge.

Utah

I-15 continues through

for . It is the main north–south connection for the state. The highway approximately follows the old alignment of US 91 from St. George to Brigham City. The highway passes through the fast-growing Utah's Dixie region in the southwestern part of the state, which includes St. George, Cedar City, and eventually most of the major cities and suburbs along the Wasatch Front, including Provo, Orem, Sandy,

, Layton, and Ogden. Near Cove Fort, I-70 begins its journey eastward across the country. The Interstate merges with I-80 for about from South Salt Lake to just west of Downtown Salt Lake City and also merges with I-84 from Ogden to Tremonton. Along nearly its entire length through the state, I-15 winds its way along the western edge of a nearly continuous range of mountains (the Wasatch Range in the northern half of the state). The only exceptions are north of Cove Fort and when it passes between Cedar City and St. George, known as the Black Ridge, a transition zone of drastic change in elevation and climate, an area where the eastern Great Basin, Colorado Plateau, and

Mojave Desert The Mojave Desert (; ; ) is a desert in the rain shadow of the southern Sierra Nevada mountains and Transverse Ranges in the Southwestern United States. Named for the Indigenous peoples of the Americas, indigenous Mohave people, it is located pr ...

converge.

Idaho

I-15 passes through

for . I-15 crosses the

state line in Oneida County. The highway runs through Pocatello, Blackfoot, and Idaho Falls, intersecting with I-86. The last county in Idaho that I-15 passes through is Clark County. Finally, the Interstate reaches the

state line at Monida Pass.

Montana

I-15 continues onward through of

through the cities of

Butte In geomorphology, a butte ( ) is an isolated hill with steep, often vertical sides and a small, relatively flat top; buttes are smaller landforms than mesas, plateaus, and table (landform), tablelands. The word ''butte'' comes from the French l ...

, Helena, and Great Falls, intersecting with I-90, I-115, and I-315. At Sweet Grass, I-15 terminates upon crossing the Canadian border into the province of

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

; however, I-15 signage is present on Alberta Highway 4 southbound from Lethbridge to the Canadian border.

History

I-15 was constructed along the route of US 91. Once I-15 was relatively intact, US 91 was decommissioned, except for one part in Northern Utah / Southern Idaho where I-15 instead followed the route of former US 191. I-15 originally had two suffixed routes. In California, I-15 had an eastern branch bypassing San Bernardino, which was designated I-15E. I-15E was renumbered and is now I-215. Present day routing of I-15 in California was originally given "I-15W" as its title while it was under construction (the original asphalt portions from Temescal Canyon to Ontario Avenue were dubbed I-15W on maps until 1974), but was never officially signed as such. In Idaho, I-15 had a western branch near Pocatello that connected I-15 and I-84 (then I-80N). This highway was designated I-15W. It is now the western I-86.

Growth along route

Since the construction of I-15, California, Nevada, and Utah have consistently ranked in the fastest-growing areas of the United States. As a result, the route of I-15 has substantially increased in population and commuter traffic has increased the traffic burden on the freeway. Current population estimates are that more than 75 percent of the population of Utah, 19 percent of the population of California, and more than 70 percent of the population of Nevada live in counties where I-15 is the primary

. Similarly, in California, I-15 is seeing more commuter traffic due to the growth of the

communities of Hesperia, Victorville, and Barstow. In Utah, I-15 has been under near-constant construction in the Wasatch Front, and future plans released by the Utah Department of Transportation (UDOT) indicate that this will continue in the north ''and'' the far south of the state as well, due to the extremely rapid growth of Washington County and surrounding areas. In like manner,

in Nevada has seen growth along I-15, and in all of the states that it currently serves, it has recently been or is currently in the process of being widened. The portions in Arizona, Idaho and Montana have retained their rural, long-haul character. Although Arizona has also grown substantially since the construction of I-15, this

highway A highway is any public or private road or other public way on land. It includes not just major roads, but also other public roads and rights of way. In the United States, it is also used as an equivalent term to controlled-access highway, or ...

serves only the isolated corner of northwestern Arizona. Due to this rapid area growth, the I-15 corridor is the focus of several mass transit projects. The Las Vegas Monorail, '' FrontRunner''

commuter rail Commuter rail or suburban rail is a Passenger train, passenger rail service that primarily operates within a metropolitan area, connecting Commuting, commuters to a Central business district, central city from adjacent suburbs or commuter town ...

system, and TRAX light rail in

are mass transit lines loosely parallel to I-15 that are now in operation. The Los Angeles–Las Vegas corridor has long been proposed as a high-speed maglev train route to relieve highway congestion. Proposals from as early as the 1970s were succeeded by the California–Nevada Interstate Maglev project, which was studied from 2004 to 2010 but never realized.

Amtrak The National Railroad Passenger Corporation, Trade name, doing business as Amtrak (; ), is the national Passenger train, passenger railroad company of the United States. It operates intercity rail service in 46 of the 48 contiguous United Stat ...

ran a conventional passenger rail service between the two cities, named the '' Desert Wind'', from 1979 to 1997. The Brightline West line, a conventional

high-speed rail High-speed rail (HSR) is a type of rail transport network utilising trains that run significantly faster than those of traditional rail, using an integrated system of specialised rolling stock and dedicated railway track, tracks. While there is ...

service under a private operator, broke ground in 2024 and is scheduled to commence in 2028 with service between Rancho Cucamonga and Las Vegas. It will use the median of I-15 for most of its route and reach speeds of up to .

Future

The segment signed as SR 15 from I-5 to I-8 in

is planned to be redesignated as part of I-15 once this segment is completely converted to Interstate standards, namely where the freeway's interchange with SR 94 is concerned. The interchange currently has left-exits and blind merges, and is due to be updated with a widening of both SR 15 and SR 94. At that time, SR 15 is planned be resigned as part of I-15. The remaining portion of SR 15 conforms with Interstate standards.

Junction list

; California : in

: in Murrieta : in

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

: in San Bernardino : in Hesperia : in Barstow ; Nevada : in Enterprise : in

. I-15/US 93 travels concurrently to northeast of North Las Vegas. ; Arizona : No major junctions ; Utah : south-southwest of Cove Fort : north-northeast of Holden. The highways travel concurrently to Scipio. : in Santaquin. The highways travel concurrently to Spanish Fork. : in Provo : in Lehi. The highways travel concurrently to Draper. : in Murray : in South Salt Lake. The highways travel concurrently to

. : in Salt Lake City : in North Salt Lake : in North Salt Lake : on the West Bountiful– Bountiful city line. The highways travel concurrently to Farmington. : in Riverdale. The highways travel concurrently to Tremonton. : on the Perry– Brigham City city line. ; Idaho : north-northwest of

Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

. The highways travel concurrently to Pocatello. : northwest of McCammon. The highways travel concurrently to Pocatello. : in Chubbuck : southwest of Blackfoot : in Blackfoot. The highways travel concurrently to Idaho Falls. : in Idaho Falls. The highways travel concurrently through Idaho Falls. ; Montana : in

. The highways travel concurrently through Butte. : in Butte : in Helena. I-15/US 287 travels concurrently to northeast of Wolf Creek. : in Great Falls. I-15/US 89 travels concurrently to northeast of Vaughn. : in Shelby : at the Sweetgrass-Coutts Border Crossing in the Canadian border east-northeast of Sweet Grass

Auxiliary routes

* Inland Empire, California – I-215 *

Las Vegas, Nevada Las Vegas, colloquially referred to as Vegas, is the most populous city in the U.S. state of Nevada and the county seat of Clark County. The Las Vegas Valley metropolitan area is the largest within the greater Mojave Desert, and second-l ...

– I-215, I-515 (former) *

Salt Lake City, Utah Salt Lake City, often shortened to Salt Lake or SLC, is the List of capitals in the United States, capital and List of cities and towns in Utah, most populous city of the U.S. state of Utah. It is the county seat of Salt Lake County, Utah, Salt ...

– I-215 *

Butte, Montana Butte ( ) is a consolidated city-county and the county seat of Silver Bow County, Montana, United States. In 1977, the city and county governments consolidated to form the sole entity of Butte-Silver Bow. The city covers , and, according to the 2 ...

– I-115 * Great Falls, Montana – I-315 (unsigned)

References

External links

* * https://web.archive.org/web/20030626140609/http://www.dot.ca.gov/dist11/facts/I-15managed.pdf * 2005 Rand McNally ''The Road Atlas 2005''- newest feature- interstate mileage by state ; California
California Highways: SR 15

; Arizona
I-15 Completed December 14, 1973
{{DEFAULTSORT:I15 15 U.S. Route 91